Devices of the type discussed here are bandages wound tightly around the body part, or liners which are pulled over an amputation stump. The liners have a certain wall thickness and have the function of forming a padding interlayer, adapting or adapted to the amputation stump, between the amputation stump and the inner face of a prosthesis shaft. The prosthesis shaft is part of a prosthesis which replaces the amputated part of an extremity of the patient.
The transmission of electrical signals between the amputation stump and the outer side of the liner may be envisioned for many reasons. For instance, it may be expedient to transmit electrical signals from the skin of the amputation stump outward, in order to control the function of the prosthesis. In this case, the electrodes may be myoelectrical electrodes which pick up muscle contraction signals at suitable points on the amputation stump, so that it is possible to control corresponding prosthetic limbs. Myoelectrical control of prostheses is known in particular for arm and hand prostheses, but may also be used for leg and foot prostheses.
It may furthermore be expedient to electrically determine the surface resistance of the skin of the amputation stump by measuring a flow of current between two or more electrodes, or electrode sections. In this way, for example, it is possible to determine whether the skin of the amputation stump inside the liner is perspiring, which may impair the purchase of the liner on the amputation stump—and therefore the purchase of the prosthesis. It is furthermore possible to determine the application pressure of the amputation stump on the inner face of the liner using electrodes, for example so as to be able to respond to a decrease in the mass of the amputation stump while the prosthesis is being worn.
On the other hand, it may be expedient to transmit electrical signals from the outer side of the liner onto the skin of the amputation stump, for example in order to stimulate a muscle contraction of the amputation stump when the wearer of the prosthesis is in a passive, for example seated, position for a prolonged period of time.
A liner which is provided for accommodating myoelectrical electrodes is known by U.S. Pat. No. 5,443,525. To this end, a nonmetallic, flexible and soft flat pad, in which there are a large number of discrete conductive electrodes, is adhesively bonded into a window of the prosthesis shaft. The liner preferably consists of silicone, a nonconductive flexible synthetic material. The electrodes may be formed from a mixture of silicone and carbon or of silicone and silver, the electrodes respectively being surrounded by nonconductive silicone. The electrode arrangement is therefore adhesively bonded by means of the pad onto the inner side of the liner, and is accessible through the window of the liner so that the myoelectrical signals picked up by the electrodes can be fed outward through the window for evaluation and control. This arrangement is elaborate to produce and has limited wearing comfort. Furthermore, the window of the liner requires particular sealing outlay when the liner—as is often usual—must be airtight in order to hold the liner on the amputation stump with the aid of a reduced pressure formed inside the liner. The reduced pressure must in this case be maintained by the liner against the weight of the moving prosthesis.
US 2009/0216339 A1 discloses a similar liner, in which a conductive insert provided for connection to an electrode is fitted into a corresponding opening of the liner and bears on the outer side of the liner at the edge of the opening with a flange-like edge. The insert is adhesively bonded to the liner. The height of the insert may be selected in such a way that it corresponds to the thickness of the liner. Primarily, however, the intention is that the insert protrudes inward beyond the inner face of the liner in order to press against the tissue of the amputation stump. On the inner side of the liner, an air gap or a gap filled with adhesive is formed between the insert and the wall of the liner. The disadvantages mentioned above also apply for this design, namely increased outlay for the production of airtightness of the adhesive bond, which may be exposed to high mechanical stresses. With high production outlay, therefore, functional reliability is not fully ensured.
This problem also arises in the solution according to DE 20 2006 007 460 U1, in which a special holder for conductive electrode sections, which bears with a flange-like edge on the inner side of the liner, is provided.
DE 10 2010 005 462 A1, not yet published at the priority date of the present application, describes a liner in which a conductive section is integrated into the material of the liner and forms a unitary, continuously aligned inner face with the nonconductive material of the liner. The nonconductive material of the liner is preferably a polymer, in which case the conductive section may be inserted into the material before polymerization of the nonconductive material so that the conductive section is connected to the material of the liner during polymerization thereof to form a unitary part, and the smooth continuous inner face is formed. The conductive section may in this case also consist of the per se nonconductive material of the liner, which has been made electrically conductive with additives. The conductive section may be polymerized together with the material of the liner. The conductive section is in this case used for electrical connection of the skin surface of the amputation stump to a separate electrode, which is arranged directly on the other side of the conductive section and picks up electrical signals, for example myoelectrical signals, from the skin of the amputation stump, or alternatively generates excitation signals which are transmitted via the conductive section onto the skin. To this end, the liner has for example a reception chamber on the outer side of the electrically conductive section, into which an electrode can be mechanically inserted. The shaping which this requires for the liner entails additional outlay.
The problems arising with liners for an amputation stump also exist in a similar form for bandages which are wound around a body part, for example around an extremity, around the trunk of the body, or the like.